Gay earned his fourth career PGA Tour victory and first since capturing the St. Jude Classic in 2009.

Scott Stallings entered Sunday with a five-stroke lead, but he made a series of costly missteps during the final round. After playing bogey-free over the first three days of the tournament, the 27-year-old dropped a shot on three separate holes Sunday.

He missed a 2-foot par putt on No. 7, then bogeyed again on the 16th to fall into a tie with Gay, Howell and rookie David Lingmerth at minus-25.

Still, Stallings appeared to be in control after finding the fairway off the tee on the par-5 18th. Needing a birdie to win, he sent his approach into the water left of the green and eventually stumbled to a bogey, which sent Gay, Howell and Lingmerth to a playoff at 25-under 263.

"I just hit a bad shot at a bad time," Stallings said.

Lingmerth was eliminated after he bogeyed the first extra hole, while Gay and Howell parred to advance.

Playing the par-4 10th at the Palmer Private Course, Howell found the rough off the tee and sent his second shot into a greenside bunker. Gay, meanwhile, placed his first squarely in the fairway and dropped his approach within 10 feet. When Howell failed to get up- and-down, Gay had two shots to win it, although he only needed one; sinking the short birdie putt to finish in first.

"I'm still in a little bit of shock," Gay said. "It kind of happened so fast there at the end the way things went down. Last year was a struggle. It was a long year, a lot of work. I just wanted to come out this year kind of refocused, recharged, and believing in myself."

Gay fired a 63 during the final round, Howell shot 64 and Lingmerth turned in a sparkling 62 to overtake Stallings, who carded a 70 and ended tied for fourth place with rookie James Hahn at 24-under. Hahn eagled the last to notch a 62.

Phil Mickelson made his season debut and finished tied for 37th at 17-under. The lefty was recovering from flu-like symptoms and as his health improved, so did his play. He shot even-par on the opening day and followed with rounds of 67, 66 and 66.

"I was rusty starting the year, and I had a great four days here where I can work on my game with perfect weather and wonderful golf courses, where I could build some momentum," said Mickelson. "... I feel a lot more confident in my game. I feel like I'm starting to play well, hit some putts on line. ..."

Nicholas Thompson carded a 64 on Sunday and ended in a tie for sixth place with Ryan Palmer (65) at 23-under, while Kevin Chappell (62) and Jason Kokrak (65) tied for eighth at minus-22.

Stewart Cink shot 68 and tied for 10th place with five others at 21-under. It marked the first top-10 finish for Cink since he tied for ninth at the Wells Fargo Championship in 2011. He hasn't won since capturing the British Open title in 2009.

Gay turned in a bogey-free round on Sunday and pulled into a tie for the lead at 24-under with consecutive birdies to start his outward nine. Stallings started his back stretch in the same fashion to reach minus-26, but Gay stayed within striking distance with another birdie on the 13th.

"The thoughts were, 'Just be aggressive, shoot as low as you can,'" Gay said. "I knew Scott was five ahead. Even with a great round, a really low round, it would be tough to catch him, if at all. I played great on the front, just tried to stay aggressive and shoot low."

After Stallings bogeyed the 16th, Gay had a chance to grab the outright lead with an eagle chance from the fringe on the last. But he sent that putt past the hole and was forced to wait for a playoff after rimming out the comeback birdie attempt from inside 10 feet.

"I felt like I gave one back with a par on 18 there," said Gay. "Was fortunate enough to feel like I had a second chance with two guys left that didn't birdie the hole. Kind of a second chance, if you will. I was happy to be in the playoff at that point."

NOTES: Stallings was forced to withdraw from this event last year due to a rib injury ... Defending champion Mark Wilson and 2012 U.S. Open champion Webb Simpson both missed Saturday's cut at 7-under and 8-under, respectively ... The pros were joined by amateurs for the tournament's first three rounds.